Inhibiting the corrosion of coppercontaining metals



United States This invention relates to a method for inhibiting corrosive attack upon copper alloys contacted by aerated, aqueous detergent solutions, and to a novel detergent composition.

Copper alloys such as brasses and bronzes usually display high resistance to corrosive attack by water or aerated, aqueous, salt solutions. Copper alloys which are highly resistant to corrosive attack, such as admiralty brass, nevertheless have been found to be rapidly corroded when contacted by aerated, aqueous solutions of commercial detergents. The art recognizes numerous organic compounds which can be used to inhibit the corrosion of metals subject to corrosive attack by aerated, aqueous solutions. Such inhibitors have been found to be generally ineffective, or only slightly effective, for inhibiting the corrosion of copper alloys contacted by aerated, aqueous solutions of commercial detergents.

It has been determined that this condition is due to the presence of builders in detergent formulations, these builders being alkali-metal polyphosphate salts, commonly sodium tripolyphosphate, sodium pyrophosphate, or sodium hexametaphosphate, or mixtures thereof. Normally, in the use of detergent compositions in machinery such as found in laundries or factories, coatings of corrosion products and other insolubles form a protective layer on metal surfaces. The presence of builders in detergents, however, prevents or removes this layer and promotes corrosion of the metallic surfaces. It has been found that such corrosion can be effectively inhibited by incorporating in the aqueous medium small amounts of certain dimer acids.

It is therefore an object of this invention to provide a novel method for inhibiting the corrosion of copper alloys contacted by aerated, aqueous, detergent solutions. Another object of this invention is to provide a novel detergent composition for use in apparatus fabricated at least in part of copper alloys. Other objects of this invention will become apparent from the following description.

In general, the dimer acids useful in this invention have been produced by heat polymerization of esters of monocarboxylic acids to esters of the dimer acids, followed by hydrolysis. Numerous examples of the dimer acids useful in the method of this invention, and the methods of preparation of such dimer acids, are described in detail in US. Patents Nos. 2,482,761 and 2,763,612. The dimer acids useful in the method of this invention are monocyclic or bicyclic aromatic dicarboxylic acids, depending upon the degree of unsaturation of the monocarboxylic acids from which the dimer acids are obtained. Thus, octadecadienoic acids polymerize to monocyclic dicarboxylic acids, while octadecatrienoic acids polymerize to bicyclic dicarboxylic acids. The cyclic dimerized acids are derivable from polyolefinic, monocarboxylic fatty acid monomers having at least carbon atoms per molecule. Such dimer acids, when used in the amount of about 0.005 to 0.1 percent by weight, in aerated aqueous solutions of commercial detergents containing polyphosphate builders, are effective for inhibiting the corrosion of copper alloys contacted by such solutions.

atent 3,267,038 Patented August 16, 1966 where R is CH (CH R is (CH COOH, n is one more than the number of CH groups between the terminal CH group and the near carbon atom of the near double bond, and m is the number of CH groups between the carboxylic group of the monocarboxylic acid and the near carbon of the near double bond.

Typical of the diethenoid acids capable of dimerization in accordance with this invention is the diethenoid linoleic acid, or A -octadecadienoic acid. This acid dimerizes in the absence of other polyethenoid acids to form the monocyclic dimeric dicarboxylic acid in which R is CH (CH and R is (CH COOH.

When triand greater ethenoid acids such as n-linolenic acids are dimerized, the dimeric acids obtained are bicyclic dicarboxylic acids having a formula such as:

when only a single acid undergoes polymerization. Typical of the bicyclic dicarboxylic dimer acid-forming monomers is the triethenoid linolenic acid, or A octadecatrienoic acid. When this is the sole polyethenoid acid present it polymerizes to form the dimer carboxylic acid of the foregoing formula.

A well-known source of these dimeric acids is the product sold by Emery Industries, Incorporated, and said to be a dilinoleic acid. The properties of these materials are as follows:

Neutral equivalent 290-310 Iodine value 95 Color Gardner 12 Dimer content, percent About Trimer and higher content, percent About 12 Monomer content, percent About 3 It will be noted that the dimeric acids as commercially produced contain about 85% dimeric acids and 12% trimeric and higher polymeric acids. Since the dimeric acids are not available in pure form, the experiments reported in this specification were conducted employing commercially available dimeric acids of about 85% purity. While the use of commercial products of 85% purity has proved to be highly satisfactory, it is expected that still better inhibition can be obtained with pure dimer acids. Especially preferred are the monocy-clic dimer acids produced from A -Octadecadienoic acid (linoleic acid).

The method of this invention is useful in protecting numerous copper alloys from corrosive attack by aerated aqueous solutions of commercial detergents containing effective amounts of polyphosphate builders. Copper alloys, having normally high corrosion resistance, which are readily attacked by aqueous, aerated, polyphosphate solutions include copper-zinc alloys containing 6090% by weight of copper, such as gilding metal, commercial bronze, red brass, spring brass, common brass, Muntz metals, and admiralty brass. Copper alloys containing minor amounts of metal such as zinc, lead, tin, aluminum, and nickel, such as forging brass, architectural bronze, aluminum brass, naval brass, nickel-aluminum bronze, aluminum bronze, and cupro-nickel, are also subject to corrosive attack and can be inhibited in accordance with this invention. The alloys protected can also contain minor amounts of manganese, beryllium or phosphorus.

It has been found that the alkali-metal polyphosphate salts responsible for accelerated corrosive attack upon normally corrosion-resistant copper alloys are the pyrophosphate, tripolyphosphate, hypophosphate, hexametaphosphate, and trimetaphosphate salts. Of these, the pyrophosphate, tripolyphosphate, and hexametaphosphate salts of sodium are especially likely to be found in commercial detergents, and result in serious corrosion problems when such detergents are employed in apparatus fabricated of copper alloys.

The effectiveness of the method of this invention for inhibiting corrosion, as well as the ineffectiveness of a wide variety of chemically similar corrosion inhibitors of the prior art, for inhibiting the corrosion of copper alloys contacted by aerated, aqueous solutions of commercial detergents has been demonstrated experimentally. First, a water solution of a commercial detergent composition containing mixed aryl alkyl sulfonates, sodium tripolyphosphate, sodium sulfate, and other com- .ponents (0.5 gram detergent per 100 millimeters of water) was prepared and divided into a plurality of Suflicient amounts of various inhibitors were added to each flask to produce an inhibitor concentration of 0.1 gram per 100 milliliters of solution. Finally, two brass strips /z inch by 3 inches) were immersed in the solutions in each flask, and air was bubbled through the solutions at a rate of 20-30 milliliters per minute for a period of 72 hours while the temperature was maintained at about 70 centigrade. Percent weight loss from the brass strips for each test are given in the following table.

TABLE I Inhibitor: Percent weight loss Blank 1.70 Dimer acid 0.25 Phthalic anhydride 0.90 Tall oil fatty acid 0.68 Linoleic acid 0.73 Triethylene tetramine 1.59 Linseed oil fatty acid 0.73 Rosin acid 1.32 Pine oil 1.78 Lithium ricinoleate 0.95

*Commercial dimer acids, about 85% dimerized linoleic acid, 15% acid monomers and trimers.

A further series of experiments was performed to establish that the effective agents causing the corrosion of normally corrosion-resistant copper alloys were polyphosphate builders usually employed in commercial detergents. These further experiments also establish that the dimer acids when employed in the method of this invention are effective for inhibiting corrosion induced by the presence of polyphosphates in aerated aqueous solutions. The results of the experiments are set forth in Table II.

TABLE II Comp., Deter., Inhib., Percent; Detergent Components Wt. Wt. Inhibitor Wt. Wt.

Percent Percent Percent Loss 100 0. 5 0. 25 $3 0. 5 -0. 11 40 Sodium sulfate 20 0. 5 0. 07 Trisodium ph0sphate 40 DB SS 40 Sodium sulfate 20 0. 5 1. 04 Sodium pyrophosphate 40 DBSS 40 Sodium sulfate 20 0. 5 Dimer 0.2 0.35 Sodium pyrophosphate 40 acid. DB SS 40 Sodium sulfate 20 0. 5 1. 33 Sodium tripolyphosphate" 40 DBSS 40 Sodium sulfate 20 0. 5 Dimer 0. 2 0. 28 Sodium tripolyphosphatc 40 acid Sodium pyrophosphate 100 O. 5 1. 75 Sodium pyrophosphate 100 0.5 Dungr 0.2 0 48 am Sodium tripolyphosphate 100 0. 5 1. 64 Sodium tripolyphosphate 100 0. 5 Din'ftt 0. 2 0. 20

1 Dodecylbenzene sodium sulfonate. 2 Commercial dimer acids, about dimerized linoleic acid and 15% monomers and trirners.

It will be noted that the dimer acids were not as effective in inhibiting corrosive attack upon copper alloys induced by the synthetic detergent compositions of Table II. This is believed to be because of the abnormally high concentration of polyphosphates in the compositions of Table II. In these experiments, the same procedures as described with reference to Table I were employed.

While the invention has been described with reference to commercial detergent solutions based upon alkaryl sodium sulfonates including polyphosphate builders, the method of this invention is useful in inhibiting corrosion produced by any detergent composition which includes polyphosphate builders.

This invention also contemplates and includes detergent compositions per se which employ polyphosphate builders and which include a small but effective amount of dimer acids to inhibit corrosion of copper alloys which would otherwise occur when the detergent is placed in aqueous solution and contacts structures fabricated of copper alloys. Thus, the detergent compositions of this invention will include any of a wide variety of cationic, nonionic, or anionic detergents which include a minor but effective amount of polyphosphate builders, and a small amount of dimer acid inhibitor. Especially preferred compositions are detergents based upon alkaryl sodium sulfonates, and including minor amounts, usually in the range of about 5-20%, of polyphosphate builders such as the alkali-metal pyrophosphate, tripolyphosphate, hexametaphosphate, trimetaphosphate, and hypophosphate salts. More preferably, the builders will be the solium salts such as sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate. A preferred detergent base is dodecylbenzene sodium sulfonate. The detergent composition will contain about 120% by weight, and preferably about 5% by weight, based upon the total weight of the detergent composition, of the aforedefined dimer acid.

A specific example of a detergent composition in accordance with this invention is as follows:

Dimer acids The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition consisting essentially of an alkaryl sodium sulfonate detergent, alkali-metal polyphosphate salts selected from the group consisting of sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate in an amount sufficient to inhibit metathesis aud about 120% by weight of the total composition of cyclic, dimerized acids having at least two olefinic linkages per molecule and being derivable from polyolefinic, monocarboxylic fatty acid monomers having at least carbon atoms per molecule.

2. A composition in accordance with claim 1 in which said detergent includes a major proportion of alkaryl sodium sulfonates.

3. A composition in accordance with claim 2 in which said sulfonate is dodecylbenzene sodium sulfonate.

4. The composition in accordance with claim 3 in which said dimeric acid is a dimer of A -octadecadienoic acid.

5. In the method of inhibiting the corrosion of coopercontaining metals in contact with aqueous, aerated solutions containing alkali-metal polyphosphate salts selected from the group consisting of sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate in amounts suflicient to promote corrosion of said copper- 6 containing metals the improvement consisting essentially of adding to the solutions about 0.005 to 0.1%, by Weight of said solution, of cyclic dimerized acids having at least two olefinic linkages per molecule and being derivable from polyolefinic monocarboxylic fatty acid monomers having at least 10 carbon atoms per molecule.

6. The method in accordance with claim 5 in which said solution is a detergent solution containing alkaryl sodium sulfonates.

7. The method in accordance with claim 6 in which said sulfonate is dodecylbenzene sodium sulfonate.

8. The method in accordance with claim 7 in which said dimerized acid is a dimer of A -octadecadienoic acid.

References Cited by the Examiner UNITED STATES PATENTS 2,618,604 11/1952 Schaefier et al. 252389 XR 2,763,612 9/1956 Raifsnider et al. 252-389 XR 2,773,032 12/1956 Cantrell et al. 252389 XR 2,861,954 11/1958 Ruff 252138 XR 2,954,347 9/1960 John et al. 252-138 XR LEON D. ROSDOL, Primary Examiner.

JULIUS GREENWALD, Examiner.

J. T. FEDIGAN, Assistant Examiner. 

1. A COMPOSITION CONSISTING ESSENTIALLY OF AN ALKARYL SODIUM SULFONATE DETERGENT, ALKALI-METAL POLYPHOSPHATE SALTS SELECTED FROM THE GROUP CONSISTING OF SODIUM PYROPHOSPHATE, SODIUM TRIPOLYPHOSPHATE, AND SODIUM HEXAMETAPHOSPHATE IN AN AMOUNT SUFFICIENT TO INHIBIT METATHESIS AND ABOUT 1-20% BY WEIGHT OF THE TOTAL COMPOSITION OF CYCLIC, DIMERIZED ACIDS HAVING AT LEAST TWO OLEFINIC LINKAGES PER MOLECULE AND BEING DERIVABLE FROM POLYOLEFINIC, MONOCARBOXYLIC FATTY ACID MONOMERS HAVING AT LEAST 10 CARBON ATOMS PER MOLECULE. 